1. Field of the Invention
This invention relates to laser remote sensing. More particularly, it relates to the remote detection and measurement of selected gases in the atmosphere or of trace gases emitted into the atmosphere.
2. Description of the Prior Art
The most common technique employed for laser remote sensing involves differential-absorption lidar (DIAL). DIAL transmits two or more different wavelengths toward a distant target and detects backscattered light using a telescope and optical detector. The technique of DIAL for the detection of trace gas clouds in the atmosphere has been known for many years.
Successful detection of a trace gas cloud requires that the gas being detected has a strong optical absorption of one of the DIAL laser wavelengths, and that lasers exit at the trace gas absorption wavelengths to permit DIAL or lidar detection of the backscattered optical signal. Previous attempts to detect gas clouds emitted by common nitrogen-based munitions explosives such as TNT and RDX have not been successful because the vapor pressure of TNT and RDX is extremely low. Attempts to use a DIAL remote sensing system were not successful because the optical depth (i.e., gas concentration times the optical attenuation coefficient of the gas) was negligible or very small. The remote detection of triacetone triperoxide (TATP) explosives had not yet been conducted successfully. It was not previously known that TATP had a high vapor pressure and strong optical absorption spectra that could be thus used for remote optical or DIAL detection of a TATP gas cloud.
Thus there is a need to incorporate DIAL technology into a system for remotely detecting the presence of TATP.
However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in this art how the identified needs could be met.